0.前言

马上圣诞节了，今天推一篇用MATLAB画圣诞树的，效果如下图所示：

1.准备工作

因为这次用的是MATLAB，不像PYTHON一样需要装一些依赖库，要实现本文的效果，只需安装MATLAB即可。

2.动起手来

2.1 画树

要画圣诞树，首先...画棵树，然后再想办法来点缀它。

close all;clear;clc
% setup
snow=450; % number of snow flakes [0 .. 5000]
% draw tree
h=0:0.2:25; %vertical grid
[X,Y,Z] = cylinder(tree(h)); %produce a tree formed cylinder
Z=Z*25; %scale to the right heigth
%Add some diffusion to the surface of the tree to make it look more real
treeDiffusion=rand(126,21)-0.5;%some horizontal diffusion data
%add diffusion to the grid points
for cnt1=1:21
for cnt2=16:126%starting above the trunk
%get the angle to always diffuse in direction of the radius
angle=atan(Y(cnt2,cnt1)/X(cnt2,cnt1));
%split the diffusion in the two coordinates, depending on the angle
X(cnt2,cnt1)=X(cnt2,cnt1)+cos(angle)*treeDiffusion(cnt2,cnt1);
Y(cnt2,cnt1)=Y(cnt2,cnt1)+sin(angle)*treeDiffusion(cnt2,cnt1);
%some Vertical diffusion for each point
Z(cnt2,cnt1)=Z(cnt2,cnt1)+(rand-0.5)*0.5;
end
end
%draw the tree
h0 = figure('Units','inches');
pos = h0.Position;
pos(1) = 1; pos(2) = 1;
pos(3) = 7; pos(4) = 7;
h0.Position = pos;

2.2 服道化

下一步，给树打个光，填个色，角度调整一下来点三维效果，把坐标系显示去掉，然后一棵绿油油的树就出现了。

%Use as nice green color map (darker at the bottom, lighter at the top)
r=(0.0430:(0.2061/50):0.2491)';%red component
g=(0.2969:(0.4012/50):0.6981)';%green component
b=(0.0625:(0.2696/50):0.3321)';%blue component
map=[r,g,b];%join in a map
for cnt=1:6
%change the lower part to brown for the trunk
map(cnt,:)=[77,63,5]/265;
end
colormap(map)%set the map
view([-37.5,4])%Change the view to see a little more of the Actual 3D tree
lighting phong %some nice lighting
shading interp %remove grid and smoothen the surface color
axis equal %takes care of display in the right proportion
axis([-10 10 -10 10 0 30]) %give some more axis space (for the snow later)
axis off %but don't show axis
hold on %to draw the rest
title('Merry Christmas','color','w',...
'fontsize',25,...
'fontweight','Bold'

接下来，把图像底色调一下，用一个五彩斑斓的黑加点星空蓝当背景（此处在某甲方选手不断提出色彩需求后最终确定的颜色，致谢！）

然后再摆几个小礼物盒子在树下，这过节气氛杠杠的。

set(gcf,'color',[22 32 51]./255)
% Presents
%Draw some presents around the tree (each with random color)
drawPresent(2,-4,0,3,3,2);
drawPresent(-4,3,0,2,3,1.5);
drawPresent(5,3,0,4,3,3);
drawPresent(-14,-5,0,6,3,1);
drawPresent(-9,-10,0,2,2,2);
drawPresent(0,4,0,4,3,3);
drawPresent(-6,-13,0,3,3,3);

2.3 雪花飘飘

最后，关键部分，撒点雪花，再画点彩灯到图上，调整三维图像的角度，来点动画效果，结束战斗！

% Snow
%create some random 3D coordinates for the snow (amount as in setup above)
snowX=(rand(snow-100,1)*25-12.5);
snowY=(rand(snow-100,1)*25-12.5);
snowZ=(rand(snow-100,1)*27);
color0 = jet(length(snowX));
%Note:Some flakes will end up IN the tree but just can't be seen then
for ii = 1:length(snowX)
plot3(snowX(ii),snowY(ii),snowZ(ii),'*','color',color0(ii, :),'markersize',randi(15))%plot coordinates as white snow flakes
% plot3(snowX(ii),snowY(ii),snowZ(ii),'*','color',color0(ii, :))%plot coordinates as white snow flakes
end
h=plot3(snowX,snowY,snowZ,'w*');
im = {};
for ii = 1:180
if mod(ii,3) == 0
h.Visible = 'off';
snowX=(rand(snow,1)*25-12.5);
snowY=(rand(snow,1)*25-12.5);
snowZ=(rand(snow,1)*27);
h=plot3(snowX,snowY,snowZ,'w*');
% pause(0.25)
else
view([ii,4])
% pause(0.1)
end
if ii > 85
frame = getframe(gcf);
im{ii} = frame2im(frame);
end
end

2.4 输出gif文件

此处有知识点！敲黑板！！如何清除cell数组中的空元素。

file2write = 'chris.gif';
for ii = 1:length(im)
[A, map] = rgb2ind( im{ii}, 256);
if ii == 1
imwrite(A, map, file2write, 'gif','LoopCount',Inf,'DelayTime', 0.12);
else
imwrite(A, map, file2write, 'gif','WriteMode','append','DelayTime', 0.12);
end